Chevy hydroboost conversion - Diesel Forum - TheDieselStop.com
7.3L IDI Diesels (Not Power Strokes) Technical discussion of topics related to vehicles powered by the 7.3 Liter In-Direct Injection Navistar engines.

 
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post #1 of 6 (permalink) Old 11-18-2008, 12:14 PM Thread Starter
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Chevy hydroboost conversion

That's it, last week I finally got sick of the stock vacuum-assisted brakes, and decided to do something about it - hello hydroboost conversion! From start to finish the install took me about 6 hours, including the tools cleanup afterwards. A few notes:

1) the pushrod is 2.5" too long, to correct for this the booster needs to be offset from the firewall. I ended up with 2-1/4" spacers this bringing the pedal up 1/4" at the pushrod pivot and about 1" at the pedal pad. The stock studs that come with the booster are too short for that, so I just replaced them with 3.5"-long 3/8" grade-8 bolts from Lowe's.

2) the the bolt patter of the Chevy plate is near identical to the Ford one, but the booster is about 3/4" higher between the holes, to correct for this the spacers at the bottom holes need to be about 1/8" longer than the ones for the middle holes, this tilts the booster and the master cylinder a bit more and makes for a near straight pushrod. The top two holes of the hydroboost mounting plate can be left unused, however I'm planning on drilling my firewall for them if there ain't nothing under the dash that can interfere (haven't really looked into it yet).

3) pressure hoses for a Superduty of the same year as the truck undergoing surgery (1990 in my case) are a direct bolt-on to both the PS pump and the hydroboost unit, but need a bit of reshaping of the hard lines so the hoses end up with nice and smooth bends. You'll need just the pressure hoses, they are about $45 for both from AutoZone, you reuse your stock return line from the PS gearbox, but add another one (3/8" hose) from the hydroboos to the PS pump. I was lucky enough to have a pump with two return ports in the plastic tank, someone must have replaced the PS pump prior to me obtaining the truck as this is not stock setup for a vacuum-boosted truck - you will most likely have to either swap your tank out for one from an F450 PS pump, or add a t-ee fitting between your PS gearbox return line and the PS tank and connect the return line from the brake booster to that t-ee.

4) the master cylinder can be reused, but needs some modifications - the holes for the booster studs need to be elongated outwards a bit as the hydroboost studs are a bit further apart than those on the vacuum setup. Also the master cylinder piston bore for the booster plunger is very deep, much deeper than what the hydroboost needs, so a spacer will need to be fabbed up that is about 1" long and 3/8" or so in diameter - this slides in the piston bore between the piston and the booster plunger, the plunger end still resides about 1/4" deep in the piston bore so it will not slip off sideways or anything like that.

5) the eye in the pushrod where it slips on the pedal stud is just a bit on the small side, take a Dremel to it and it's fixed in about a minute. However, if you got a brake switch that mounts on the pedal, your brake lights will now not work. To correct for this I slightly elongated the eye of the pushrod, this way the rods slides back a tiny amount when brakes are applied and actuates the switch.

Now the results of that - turns out that Thursday night I didn't measure the piston bore spacer right, so my brakes were dragging a bit, drove it like that for good 20 miles on Friday, but nothing overheated and if anything the rotors got nicely polished. Also, I forgot that this particular hydraulic booster had developed a leak through the pushrod seals, so when I replaced the seals last year the whole thing started getting sticky at the end of its free travel. So Saturday I trimmed the piston bore spacer to the correct length and added a helper spring to the pedal (like some old hydroboosted Chevy trucks have from the factory) - all is good now, everything works like it should. Pics:










That's it - not too complicated, just a bit of PITA to tighten down the booster to the firewall as it's a two-man job. Very brutally powerful brakes now, I better be careful till I get used to them.


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post #2 of 6 (permalink) Old 11-18-2008, 05:51 PM
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Hmmm...this thread looks strangely familiar to the one on the "other" ford diesel site...LOL!

Good job though on the install!

1985 F-350 6.9 IDI w/101k miles, RC, 4x2, DRW, 4.10 gears, ZF-5speed, 5" stack, manual glow plugs, flatbed, buckets and center console off a bronco and no soup bowl!

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1989 F-350 7.3 IDI w/66k miles, Yellow with black "Boss 302" graphics
-RC, 4x4, SRW, 4.10, 5-speed, manual GP's,hand-built grille guard
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post #3 of 6 (permalink) Old 11-18-2008, 09:51 PM Thread Starter
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Lol, which other side, I have it posted on both of them - figures it may help others who want hydroboost but can't find F450 parts. Also, an Astor/Safari van hydroboost may be a decent choice, the pushrod length looks about right with those, but the mounting bracket will need re-drilling.


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post #4 of 6 (permalink) Old 11-18-2008, 10:17 PM
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Nice, very nice.

Makes me wonder about other applications........

1999 E-350 Cub Wagon, 7.3L Power Stroke, E4OD, 3.55
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1983 F-150 2x4, 4.9L, C-6 w/GV-OD, 3.55 Farm pickup
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post #5 of 6 (permalink) Old 11-18-2008, 11:22 PM
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Thanks for the information. I would like to find the F450 setup. I like your concept. Good job on the install.

Vinnie

1994 F-350 7.3 IDIT, Dually crew
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post #6 of 6 (permalink) Old 11-19-2008, 12:29 AM Thread Starter
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The F450 setup install exactly the same way, but without the spacers between the booster and the firewall - you'll still have to grind on the master cylinder to make it fit on the booster, unless you go with an F450 master, which is actually not such a great idea as the F450 has disc brakes in the rear and those take more fluid displacement than your stock drum wheel cylinders.


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